Method of short-time digesting in sulfite or sulfate digesters



J."K. HUTHS. METHOD OF SHORT HME DI GESTING IN SULFITE 0R SULFATE DIGESTEBS. APPLICATXOH FILED MAR-10.!919.

Patented Feb. 15, 1921' JOEAHNES KARL RUTHS, OI DJ'UBSHOLH, SWEDEN, ASSIGNOB TO AKTIEBOLAGIT VAPOIBAGKUMULATOR, OF STOCKEOLM, SWEDEN.

IETHOD OI SHORT-TIME J JIGESTING IN SULIITE OR SULFATE DIGEBTBBS.

To allwhom itmay comem:

Be it known that I JOHANNES KARL RUTHs, subject of the King of Sweden, residing at D ursholm, Sweden, have invented certain new and useful Improvements in Methods of Short-Time Di esting in Sulfite or Sulfate Digesters, of w ich the followin is a specification.

%n in Patent No. 1,292,080, granted to me on an. 21, 1919, an arrangement is described by means of which the total time for treatin a batch in sulfite boilers may be reduce by a shortening of the steaming period, an equalization of the variations in load occurring in the boiler house being obtained at the same time.

My present invention relates to an im provement for obtaining a further considerable increase of the advantages gained by an arrangement according to the abovenamed patent.

Whereas according to the above-named patent a saving of time could be obtained only by a shortening of the so called steaming process, according to the present Invention the same method has been applied also to the carrying out of the digesting per 8c. Figure 1 in the accompanying drawing shows the principle of carrying out my new method. Fig. 2- is a boiling diagram; Fig. 3 is a diagranr to illustrate my new method applied to a plant with four digesters.

S is the quantit of steam required for the steaming, and denotes the quantity of steam required for the digesting. The diesting takes place in the following manner. in the period between the steaming and the starting of the digesting process the and required for the digesting is run into the digestcrs, said acid absorbin the heat 1mparted to the chips so that t ie temperature of the acid is somewhat increased. In most cases this temperature will be about 50 at the time a. At the end of the digesting period, 2'. 0., at the point D, the temperature of the acid genera ly amounts to about 140.

The chemical process in the boiler only commences upon the acid having reached the temperature of about 108, at the point 0. The time 11-1: is called the startin period of the boiler. while the timer-u correspom'ls to the true tune of boilmg. If it is now desired to reduce the time (Ii-b Specification of Letters Patent.

Patented Feb. 15,- 1921.

Application fled March 10, 1919. Serial No. 281,704.

required for the whole boiling period, it IS evident that such a reduction may be effected only during the time (1-0, a reductron of the time cb causing an impairment of the quality of the mass, or great losses.

It is assumed that the present case per tams to a so called indirect boiling, i. e., the heat of the steam is transmitted to the acid by means of tubes. It is to be observed, however, that the principle of the invention may also be applied to indirect boiling, the same be1ng obviously independent of the carrying out or not of a steaming process previously to the boiling.

In indirect boiling the line rl-e shows how the pressure of the boiler is nearly maintained. As will be seen, the pressure in the starting period increases comparatively rapidly up to the maximum pressure allowed, or generally 4 to 6 kilograms above atmospheric, this pressure being then maintuined constant by distillations during the entire boiling process; It will be seen from the diagram that the boiler pressure is increasing much more rapidly than the corresponding saturation temperature of the water, this depending on the quantity of free sulfurous acid accumulating in the upper part of the boiler and increasing the pressure.

Whereas heretofore steam of constant pressure has been always used corresponding nearly to the maximum pressure of the boiler, or about 6 kilograms for the carrying out of the entire boiling process, this method aims at the employment of steam of a considerably lower pressure during the starting period. This steam is taken from the steam accumulator mentioned in the above-named patent, and the same conscriuently falls in the course of the process.

n equalization of the steam impulses being thus obtained between the boiler house and the boiler by the use of the steam accumulator, the quantity of steam B suppliedduring the starting period may be chosen considorably higher than at present. the time being thereby reduced in a corresponding degree.

Obviously. not the pressure in the boiler but the difference in temperature between the steam at the instant of condensation and the temperature of the acid i decisive for the transfer of heat between the steam in the tube and the acid in the boiler.

Now, in many cases, it will be found that with the present arrangement it is not possible to force a sutlieient quantity of steam through the tubes. these ha vine been dimensioned for relatively small quantities of steam with regard to the boiler house. As is well known. however, the drop in pressure in a team conduit with a certain qnalr tity or steam is inversely proportional to the 5th power of the diameter, only a small increase of the latter thus being sutiicient to enable the forcing of a considerably larger quantity of steam through the tube than at present without exceeding a very small drop in pressure. At the same time the pressure in the tube along the entire length thereot' is kept about the same as the initial pressure, whereas under the conditions hitherto prevailing the pressure is apt l0 fall rapidly. Thus, the average temperature of the tube becomes considerably higher, if the diameter is somewhat increased.

Fig. 2 iilustrate the appearance of the boiling diagram when using the arrangements suggested above. 5 again corresponds to the quantity of steam requisite for the steaming operation, r!-(.' being the starting period; the diagram for the boiling time proper, cl1. is the same as before. In Fig. 2 it is assumed that during the first period of the boiling. while the pressure in the boiler is still low, a quantity of steam T is admitted directly into the acid, in addition to the steam admitted into the tubes.

Fig. 3 indicates how this method is working as applied to a plant with tour boilers and with a total time for treatment, which from the original of 20 hours has been reduced to 17 hours by the present invention. In the diagram the bottom load represents the quantity of steam requisite for the cone pleting of the boiling, the tops partly giving the quantities of steam for the steaming operation. and partly the quantity of steam required for the starting up to 108. K shows the quantity of steam delivered from the boiler, and. as will be seen in the present case, a complete equalization of the same is taking place. the working of the boiler being thereby rendered practically uniform. The accumulator is charged during the time (1-6, discharged during the time bc, charged anew during the time c-d and discharged during the time d-e, charged again during the time cf and so on. The charging condition of the accumulator is ind]- rated in the upper part of the diagram.

By extending; the method set forth in the above-named patent as indicated. a further considerable shortening of the treating time for the boilers. or an increase of the out put of the plant may be obtained by the arrangements described in the above named patent. While on one side, only about 5U minutes to an hour could be saved by steanr ing from the accumulator alone, on the other side an estimation of the present case will show that as much as three hours may be saved. which with an original treating time of 19 hours brings about an increase in the output of the plant of not less than 15",. Thus. in many cases the output of a sultite plant with 5 or more boilers will be increased in the same degree by the installation of a steam accumulator as by the installation of a new boiler; as in the lirst case it will not be necessary to enlarge the boiler house, the old one answering its purpose and being, moreover. considerably unloaded. it is evident, that the capital for a plant with an accumulator will be considerably less than the capital required for any other enlargement. great savings in steam and coal being obtained in addition thereto.

Obviously, the views (ltIHUllStI'tllt'tl above pertain also to a so called basic boiling of cellulose (sulfate plant), independently of steaming being used or not as well as independently of whether direct or indirect steam is employed for the boiling.

Claim:

The method of shorttime digesting in sullite or sulfate digcsters. which consists in elieeting both the steaming and the starting operation with steam of low pressure obtained from an accumulator connected with the digester. and then completing the digesting operation with steam of higher pressure as supplied by the steam generating plant.

In testimony whereof I ailix my signature in presence of two witnesses.

JOHANNES KARL RUTHS.

\Vitnesses:

M. J. VARLIN, ESTER MATISSON. 

